From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Mon, 6 May 2002 02:39:01 +0000 (+0000)
Subject: Reorder snapshot checks to save a couple comparisons in the common case,
X-Git-Tag: REL7_3~1549
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=1cf693ab86b3c3952b441de5f57d9a9e0a925b12;p=postgresql

Reorder snapshot checks to save a couple comparisons in the common case,
where the tuple's xmin or xmax is older than the snapshot xmin.  There
is no need to check it against snapshot xmax in that case.
---

diff --git a/src/backend/utils/time/tqual.c b/src/backend/utils/time/tqual.c
index ac06d91dc4..ba052e5f77 100644
--- a/src/backend/utils/time/tqual.c
+++ b/src/backend/utils/time/tqual.c
@@ -16,7 +16,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/utils/time/tqual.c,v 1.49 2002/01/16 23:51:56 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/utils/time/tqual.c,v 1.50 2002/05/06 02:39:01 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -707,13 +707,12 @@ HeapTupleSatisfiesSnapshot(HeapTupleHeader tuple, Snapshot snapshot)
 	 * By here, the inserting transaction has committed - have to check
 	 * when...
 	 */
-
-	if (TransactionIdFollowsOrEquals(tuple->t_xmin, snapshot->xmax))
-		return false;
 	if (TransactionIdFollowsOrEquals(tuple->t_xmin, snapshot->xmin))
 	{
 		uint32		i;
 
+		if (TransactionIdFollowsOrEquals(tuple->t_xmin, snapshot->xmax))
+			return false;
 		for (i = 0; i < snapshot->xcnt; i++)
 		{
 			if (TransactionIdEquals(tuple->t_xmin, snapshot->xip[i]))
@@ -748,12 +747,15 @@ HeapTupleSatisfiesSnapshot(HeapTupleHeader tuple, Snapshot snapshot)
 		tuple->t_infomask |= HEAP_XMAX_COMMITTED;
 	}
 
-	if (TransactionIdFollowsOrEquals(tuple->t_xmax, snapshot->xmax))
-		return true;
+	/*
+	 * OK, the deleting transaction committed too ... but when?
+	 */
 	if (TransactionIdFollowsOrEquals(tuple->t_xmax, snapshot->xmin))
 	{
 		uint32		i;
 
+		if (TransactionIdFollowsOrEquals(tuple->t_xmax, snapshot->xmax))
+			return true;
 		for (i = 0; i < snapshot->xcnt; i++)
 		{
 			if (TransactionIdEquals(tuple->t_xmax, snapshot->xip[i]))